Improve output of machine oriented commands

[matklad]

Several cargo sub commands use JSON for output, for example read_manifest and metadata.

It would be nice to to customize this output (e.g. use TOML instead of JSON, redirect output to a file or control pretty printing). The relevant bit of code is here

Original discussion

[matklad]

@alexcrichton what do you think about pretty printing json by default?

We don't send JSON over the network, so there is no much gain in removing all whitespace. And with pretty printing it should be easier for humans to develop cargo-related tools.

[alexcrichton]

I'd personally prefer to have an alternate pretty-json output format, as this is in theory only really intended for pipelining between tools.

[carols10cents]

This seems like a concern that's outside of cargo's responsibilities.... for example, you can pipe compact JSON to something like jq to get pretty JSON. Given that there hasn't been a mass clamoring for this in the past year and a half, I'm going to close this :)